Passive income, in a nutshell, is money that flows in on a regular basis without requiring a substantial amount of effort to create it. The idea is that you make an upfront investment time and/or money but once the ball is rolling, there's minimal maintenance required going forward. That being said, not all passive income opportunities are created equally. For investors, building a solid portfolio means knowing which passive investing strategies to pursue. (For more, see the tutorial: Investing 101: A Tutorial for Beginners.)

1. Real Estate

Despite some ups and downs in recent years, real estate continues to be a preferred choice for investors who want to generate long-term returns. Investing in a rental property, for example, is one way to produce a regular source of income. At the outset, an investor may be required to put up a 20% down payment to buy the property, but that may not be a barrier for someone who's already saving regularly. Once reliable tenants are installed, there's very little left to do except wait for the rent checks to begin rolling in. (For more on being a landlord, see: The Pros & Cons Of Owning Rental Property.)

Real estate investment trusts (REITs) are another passive investment option for investors who aren't interested in dealing with the day-to-day burden of managing a property. One of the main advantages of a REIT is that they pay out 90% of their taxable income as dividends to investors. There is a downside, however, since dividends are taxed as ordinary income. That may be problematic for an investor who's in higher a tax bracket.

Real estate crowdfunding presents a middle-ground solution. Investors have their choice of equity or debt investments in both commercial and residential properties. Unlike a REIT, the investor gets the tax advantages of direct ownership, including the depreciation deduction without any of the added responsibilities that go along with owning a property. (To learn more about real estate crowdfunding, read: Equity vs. Debt Investments For Real Estate Crowdfunding.)

2. Peer-to-Peer Lending

The peer-to-peer lending (P2P) industry is just over a decade old, and the market has grown by leaps and bounds. For investors who want to help others while adding passive income to their portfolio, peer-to-peer lending is an attractive choice.

For one thing, there are fewer barriers to entry compared to other types of investments. For example, both Prosper and Lending Club, two of the largest P2P platforms, allow investors to fund loans with as little as a $25 investment. Both lenders also open their doors to non-accredited investors. While Title III of the Jumpstart Our Business Startups (JOBS) Act allows both accredited and non-accredited investors to invest through crowdfunding, every crowdfunding platform has its own policy regarding who can participate.

In terms of the returns, peer-to-peer lending can be profitable, particularly for investors who are willing to take on more risk. Loans pay a certain amount of interest to investors, with the highest rates associated with borrowers who are deemed the biggest credit risk. Returns typically range from 5% to 12%, and there's very little the investor has to do beyond funding the loan.

3. Dividend Stocks

Dividend stocks are one of the easiest ways for investors to create passive income because you're effectively getting paid to own them. As the company brings in earnings, part of them are siphoned off and paid back to investors as a dividend. This money can be reinvested to purchase additional shares or received as a cash payment (For more on getting ahead with dividends, read: 6 Rules For Successful Dividend Investing.)

Dividend yields can vary greatly from one company to the next, and they can also fluctuate from year to year. Investors who are unsure about which dividend-paying stocks to choose should stick to ones that fit the dividend aristocrat label, which means the company has offered increasingly higher dividends consecutively over the previous 25 years.

4. Index Funds

Index funds are mutual funds that are tied to a particular market index. These funds are designed to mirror the performance of the underlying index they track, and they offer some advantages over other investments for investors whose goal is passive income.

Index funds are passively managed, and the securities included in them don't change unless the composition of the index changes. For investors, this translates to lower management costs. Aside from that, a lower turnover rate makes index funds more tax efficient, reducing drag that would otherwise detract from returns.

The Bottom Line

Passive income investments can make an investor's life easier in many ways, particularly when a hands-off approach is preferred. The four options outlined here represent differing levels of diversification and risk. As with any investment, it's important to weigh the anticipated returns associated with a passive income opportunity against the potential for loss.

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